Welded Component Comprising Seamless Bent Pipe and Seamless Straight Pipe Sections and Methods of Manufacturing Thereof

ABSTRACT

Provided are a seamless bent pipe constituted by a bent section and straight pipe sections on both ends of the bent section, with the inside diameter at each pipe end portion being larger than the inside diameter of the bent section, and a welded component comprising a seamless bent pipe and a seamless straight pipe at one or each end of the seamless bent pipe, with the end of the seamless straight pipe to be welded to one or each end of the seamless bent pipe having the same inside diameter as the inside diameter of the seamless bent pipe, as well as methods of manufacturing them. As a result, elements suited for use in pipelines can be obtained, without unnecessarily increasing the wall thickness of the seamless bent pipe and without internal machining of the pipe end portions of the seamless bent pipe after the manufacturing thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application which claims priority benefit of U.S.patent application Ser. No. 12/561,884 filed Sep. 17, 2009 which is acontinuation of PCT/JP2008/055478 filed Mar. 25, 2008 which is based onJP 2007-090399 filed Mar. 20, 2007 the disclosure of which isincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a seamless bent pipe being an elementof pipelines, to a welded component comprising a seamless bent pipe anda seamless straight pipe(s) wherein the seamless pipe is welded to oneor each end of the seamless bent pipe, and to methods for manufacturingthem.

BACKGROUND ART

In laying line pipes (straight pipes, bent pipes and the like for use ina pipeline is collectively referred to as “line pipe(s)”) fortransporting fluids such as petroleum or natural gas, not only straightpipes but also bent pipes are used. Generally, the bent pipes are joinedto the straight pipes by circumferential welding at exact sites oflaying line pipes.

It is preferable that the straight pipe and the bent pipe to be joinedtogether are identical in inside diameter and the inside surface aroundthe circumferentially welded area between the straight pipe and the bentpipe is flush and has no step (difference in height level) so thatfluids such as petroleum or natural gas may flow smoothly through theinside of the pipelines. Therefore, it is preferable that the straightpipe and the bent pipe are identical in inside diameter as much aspossible and, for that purpose, it is necessary to produce both straightpipes and bent pipes with high dimensional accuracy.

Bent pipes are generally manufactured by hot or cold bending of straightpipes. However, on the occasion of bending, the inner-radius side of abent section becomes thicker in wall thickness and an outer-radius sideof the bent section becomes thinner in wall thickness and, therefore, itis not easy to make a pipe end inside diameter of the bent pipeidentical to a pipe end inside diameter of the straight pipe.

Furthermore, seamless pipes for line pipes are produced while primarilycontrolling an outside diameter and a wall thickness thereof, so that itis difficult to produce pipes, even when they are straight, that have novariations in inside diameter thereof. Therefore, it is much moredifficult to produce a bent pipe with high dimensional accuracy bybending such a seamless pipe which is straight (hereinafter referred toas “seamless straight pipe”) (such a bent pipe is hereinafter referredto as “seamless bent pipe”).

Japanese Patent Application Publication No. 2004-223530 proposes amethod for inhibiting bellows defective or flattening defective fromappearing on the occasion of hot or cold bending of a metallic straightpipe. However, this method is insufficient for controlling inside andoutside diameters of a bent pipe to attain the targeted dimensions.

FIG. 1 shows a configuration of a hot bending apparatus referred to asthe prior art in Japanese Patent Application Publication No. 2004-223530and an example of a bent pipe manufactured by bending. FIG. 1A shows atransitional state of bending by the bending apparatus, FIG. 1B shows aplan view of the bent pipe manufactured, and FIG. 1C shows a sectionalview of the bent pipe as seen in the direction of arrows II-II in FIG.1B.

As shown in FIG. 1A, a straight pipe 1 to be bent is passed through aninduction heating coil 2, one end of the straight pipe 1 is securelyheld by a front clamp 4 mounted on a bending arm 3 that swings around afulcrum O as the center of swing and the other end thereof is tightlyheld by a rear clamp 5, and an intermediate portion is pinched by guiderollers 6. A short pipe segment, in a pipe axis direction, of thestraight pipe 1 is induction-heated to a temperature allowing readyplastic deformation by means of the induction heating coil 2 and, at thesame time, the rear clamp 5 is pushed forward in a pipe axis directionby means of a driving system (not shown) for the straight pipe 1 tocontinuously advance in a pipe axis direction.

Then, while the short pipe segment, i.e. a heated zone 7 heated by theinduction heating coil 2 is continuously forwardly moved along a pipeaxis direction, the heated zone 7 is given a bending moment resultingfrom the swing of the bending arm 3 and is thereby subjected to bendingdeformation and, immediately thereafter, the bent portion is cooled byspraying with a cooling medium 8, such as cooling water, from theinduction heating coil 2, whereby the affected portion after bending ishardened.

In this manner, the bent pipe comprising a bent section 1 a and straightpipe sections 1 b, 1 c on both sides thereof, as shown in FIG. 1B, ismanufactured. The thus-manufactured bent pipe shows a thicker wallthickness on an inner-radius side of the bent section 1 a and a thinnerwall thickness on an outer-radius side of the bent section 1 a, as shownin FIG. 1C.

DISCLOSURE OF INVENTION

As described above, bent pipes to be used for line pipes are joined tostraight pipes at laying sites by circumferential welding. Forpreventing weld defects from developing, it is necessary that the pipeend inside diameter of the seamless bent pipe or the seamless bent pipewith seamless straight pipe (s) be identical to a pipe end insidediameter of a straight pipe for line pipes.

However, on the occasion of manufacturing a bent pipe by bending, it isinevitable for an outer-radius side of a bent section to become thinnerin wall thickness than an inner-radius side of the bent section. And,for reasons of designing pipelines, the wall thickness of the bent pipecannot be thinner than the wall thickness of the straight pipe forline-pipes and, therefore, it is necessary to produce a seamlessstraight pipe to be a bent pipe, which have a thicker wall thickness,for compensating the reduction in wall thickness on the outer-radiusside of the bent section upon bending.

Even when the wall thickness of the seamless straight pipe is thusincreased for compensating the reduction in wall thickness resultingfrom the step of bending, pipe end portions of the seamless bent pipe,even after bending the seamless straight pipe, still are the same inwall thickness as the prior-bending seamless straight pipe, becausethose portions are inhibited from being subjected to bending.

As described above, it is necessary that the pipe end inside diameter ofthe seamless bent pipe be identical to a pipe end inside diameter of astraight pipe for line pipes and, therefore, following two techniqueshave so far been employed in welding a seamless bent pipe manufacturedby bending to a straight pipe for a line-pipe.

The first technique consists in making an inside diameter of a seamlessstraight pipe to be used in manufacturing a seamless bent pipe identicalto an inside diameter of the straight pipe for a line pipe. The secondtechnique consists in making an outside diameter of a seamless straightpipe to be used in manufacturing a seamless bent pipe identical to anoutside diameter of the straight pipe for a line pipe, while internalmachining is applied to pipe end portions of seamless bent pipe thusmade to make the pipe end inside diameters of the seamless bent pipeidentical to the pipe end inside diameter of the straight pipe for aline pipe.

When the first technique, namely the technique consisting in making theinside diameter of the seamless straight pipe identical to the insidediameter of the straight pipe for a line-pipe, is employed, the outsidediameter of the seamless straight pipe for manufacturing a seamless bentpipe must be increased by a required increment in wall thickness.

However, seamless straight pipes are produced while controlling theoutside diameter and the wall thickness and, therefore, for producingseamless straight pipes differing in outside diameter, tools ofappropriate sizes fitted for targeted outside diameters are required.However, the tools for producing the seamless straight pipes areexpensive. Therefore, for employing the first technique, it is necessaryto prepare tools suited for the respective outside diameters increasedby the above-mentioned increment in wall thickness, and this causesmarked cost increases in the production of a straight pipe for aline-pipe.

Therefore, seamless straight pipes are produced by involuntarily usingexisting tools. In case where tools which are close to the desired sizebut are somewhat larger are used, the outside diameters of seamlessstraight pipes become larger than those actually required and,therefore, the wall thickness becomes unnecessarily thicker. Therefore,in case where seamless straight pipes are produced by involuntarilyusing existing tools, the addition of alloying elements in large amountsbecomes necessary for exhibiting desired mechanical performancecharacteristics in the seamless bent pipes manufactured from theseamless straight pipes thus made or, in some instances, the desiredmechanical performance characteristics cannot be obtained even when suchalloying elements are added.

On the other hand, when the second technique is employed, namely thetechnique consisting in making an outside diameter of a seamlessstraight pipe identical to an outside diameter of a straight pipe for aline-pipe, while internal machining of the pipe end portions of aseamless bent pipe after bending thereof is provided to make the pipeend inside diameter of the seamless bent pipe thus made identical to thepipe end inside diameter of the straight pipe for a line-pipe, isemployed, the bent section inside diameter of the seamless bent pipethus manufactured becomes smaller than the inside diameter of thestraight pipe for a line pipe. When internal machining is carried out toincrease the inside diameter of the bent pipe for a line pipeaccordingly, a poor workability and an increase in cost are caused.

Since, as described above, it is difficult to finish the insidediameters of seamless straight pipes to be primary blank materials withhigh dimensional accuracy in the process of production thereof, thedimensional accuracy of the inside diameter of the bent pipesmanufactured from such seamless straight pipe blanks, in the case ofmanufacturing the seamless bent pipe by bending the seamless straightpipe blanks, becomes further worsened.

Further, while seamless straight pipes are processed in a longer length,seamless bent pipes are manufactured after being cut into short-lengthpieces from seamless straight pipes and, therefore, they readily undergofluctuations in inside diameter.

An object of the present invention is to solve such problems and toprovide a seamless bent pipe having the same pipe end inside diameter asthat of a straight pipe for a line pipe and a welded componentcomprising such a seamless bent pipe and a seamless straight pipe(s)connected to the pipe end(s) of the seamless bent pipe, withoutunnecessarily increasing the wall thickness of the seamless bent pipeand without internally machining the pipe end portions of the seamlessbent pipe after the manufacturing thereof.

The present inventor made various investigations and experiments toaccomplish the above object and to obtain the seamless bent pipe capableof being joined to a straight pipe for a line pipe by circumferentialwelding and, as a result, obtained the following findings (a) to (e).

(a) For preventing weld defects from developing on the occasion ofjoining a seamless bent pipe to a straight pipe for a line pipe, it isnecessary for the pipe end inside diameter of the seamless bent pipe tobe identical to the pipe end inside diameter of the straight pipe forthe line pipe. However, that the pipe ends of both pipes are identicalin inside diameter on the occasion of welding is sufficient, no matterwhat an inside diameter of the seamless bent pipe partially is. Althoughthe above-mentioned internal machining is available for the techniqueconsisting in making the both pipe ends identical in inside diameter toeach other after manufacturing of the seamless bent pipe, such internalmachining is poor in workability and causes marked cost increases.

(b) The inventor came to realize that cold pipe expanding can beutilized as a technique of making the pipe end inside diameter of aseamless bent pipe identical to a pipe end inside diameter of a straightpipe for a line pipe.

The application of this cold pipe expanding to the pipe end portion ofthe seamless bent pipe will result in low production cost and, inaddition, provide high dimensional accuracy. This cold pipe expanding onthe pipe end portions of a seamless bent pipe may be carried out eitherafter the manufacturing of the seamless bent pipe by bending theseamless straight pipe or before bending the seamless straight pipe.Furthermore, for improving the dimensional accuracy, cold diameterreduction working may be carried out prior to cold pipe expanding on thepipe end portions of the seamless bent pipe.

(c) The thus-manufactured seamless bent pipe may be joined to a straightpipe for a line pipe by circumferential welding at actual sites oflaying line pipes. Alternatively, it is also possible to prepare inadvance a welded component comprising a seamless bent pipe and aseamless straight pipe(s) and to join this welded component to otherstraight pipe for a line pipe by circumferential welding at actual sitesof laying the line pipes.

(d) The welded component comprising the seamless bent pipe and theseamless straight pipe(s) may have either structure such that a seamlessstraight pipe is welded to one pipe end of the seamless bent pipe orstructure such that a seamless straight pipe is welded to each pipe endof the seamless bent pipe. In each case, the seamless bent pipeincorporated in the welded component has a pipe end inside diameterlarger than the inside diameter in the bent section.

And, this seamless bent pipe can be manufactured by applying either coldpipe expanding or cold diameter reduction working followed by cold pipeexpanding on the pipe end portions, as described above. At the sametime, the pipe end portion of each seamless straight pipe to beincorporated in the welded component is processed in advance by coldpipe expanding or by cold diameter reduction working followed by coldpipe expanding to make the inside diameter of the seamless straight pipesubstantially identical to that of the seamless bent pipe. Thereafter, awelded component comprising the seamless bent pipe and the seamlessstraight pipe(s) at the pipe end(s) of the seamless bent pipe can beprepared by joining the pipe end portion of the seamless bent pipe andthe pipe end portion of seamless straight pipe together bycircumferential welding.

(e) It is preferable that the cold pipe expanding on the pipe endportion of the seamless bent pipe and the cold pipe expanding on thepipe end portion of the seamless straight pipe, to be in abuttingrelation with each other, is carried out by using plugs identical indiameter.

The present invention is accomplished based on such findings describedabove, and the gist thereof pertains to a seamless bent pipe describedin (1), methods of manufacturing seamless bend pipes described in(2)-(4), a welded component described in (5) and methods ofmanufacturing a welded component described in (6)-(8). These aspects arecollectively referred to as the present invention.

(1) A seamless bent pipe comprising a bent section and a straight pipesection on each end of the bent section, wherein both pipe end portionsare larger in inside diameter as compared with the inside diameter ofthe bent section.

(2) A method of manufacturing a seamless bent pipe by bending a seamlessstraight pipe, wherein the seamless straight pipe, except for each pipeend portion, is subjected to hot bending or cold bending and thenstraight pipe sections at the pipe end portions that have not been hotor cold bent are subjected to cold pipe expanding.

(3) A method of manufacturing a seamless bent pipe by bending a seamlessstraight pipe, wherein straight pipe sections at pipe end portionsbefore bending are subjected to cold pipe expanding and then saidstraight pipe is subjected, except for the pipe end portions that havebeen subjected to pipe expanding, to hot bending or cold bending.

(4) The method of manufacturing said seamless bent pipe according to (2)or (3), wherein the straight pipe sections at pipe end portions aresubjected to cold diameter reduction working prior to cold pipeexpanding.

(5) A welded component comprising a seamless bent pipe and a seamlessstraight pipe at one or each end of said seamless bent pipe, whereinsaid seamless bent pipe according to (1) or said seamless bent pipemanufactured by any of the methods according to (2)-(4) is used, and thepipe end inside diameter of said seamless straight pipe welded to one oreach end of said seamless bent pipe is identical to an inside diameterof said seamless bent pipe.

(6) A method of manufacturing a welded component comprising a seamlessbent pipe and a seamless straight pipe at one end or each end of saidseamless bent pipe, wherein said seamless bent pipe according to (1) orsaid seamless bent pipe manufactured by any of the methods according to(2)-(4) is used, and a pipe end portion of said seamless straight pipewhich is to be welded to one end or each end of said seamless bent pipeis subjected to cold pipe expanding to make the inside diameter thereofidentical to the inside diameter of said seamless bent pipe and thensaid pipe end of said seamless bent pipe and said pipe end thusprocessed of said seamless straight pipe are joined together bycircumferential welding.

(7) The method of manufacturing the welded component comprising theseamless bent pipe and the seamless straight pipe at one or each end ofthe seamless bent pipe according to (6), wherein said pipe end portionsof said seamless bent pipe and said pipe end portion of said seamlessstraight pipe are both subjected to cold pipe expanding using plugsidentical in diameter.

(8) The method of manufacturing the welded component comprising theseamless bent pipe and the seamless straight pipe at one or each end ofsaid seamless bent pipe according to (6) or (7), wherein said pipe endportion of said seamless straight pipe is subjected to cold diameterreduction working prior to cold pipe expanding.

The methods according to the present invention can provide a seamlessbent pipe identical in inside diameter to a straight pipe for a linepipe and a welded component comprising such a seamless bent pipe and aseamless straight pipe at one or each end of the seamless bent pipe,without unnecessarily increasing the wall thickness of the seamless bentpipe and without internally machining pipe end portion(s) of theseamless bent pipe after the manufacturing thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the configuration of a hot bending apparatus of the priorart and an example of a bent pipe manufactured by bending. FIG. 1A showsa transitional state of bending by the bending apparatus, FIG. 1B showsa plan view of the bent pipe manufactured, and FIG. 1C shows a sectionalview of the bent pipe as seen in the direction of arrows II-II in FIG.1B.

BEST MODES FOR CARRYING OUT THE INVENTION

The following specific examples illustrate the subject matters of thepresent invention. The present invention is not limited by the followingexamples.

A seamless straight pipe with an outside diameter of 323.9 mm, a wallthickness of 20.0 mm, an inside diameter of 283.9 mm and a length of 500mm was prepared as a straight pipe for manufacturing a seamless bentpipe. This was subjected to cold bending at a bending angle of 90° usingthe bending apparatus shown in FIG. 1 to produce a seamless bent pipe.Then, both pipe end portions of the seamless bent pipe obtained wassubjected to cold pipe expanding using a plug to expand the inside andoutside diameters of each pipe end portion. The outside diameter, insidediameter and wall thickness dimensions of the seamless bent pipe beforeand after cold pipe expanding of the pipe end portions are shown inTable 1.

TABLE 1 Pipe end portion of seamless bent pipe Outside diameter Wallthickness Inside diameter (mm) (mm) (mm) ODb WTb IDb Before pipe 323.920.0 283.9 expanding After pipe 329.2 20.0 289.2 expanding

Further, seamless straight pipes were cut from a longer straight pipefor a line pipe to prepare seamless straight pipes with an outsidediameter of 323.9 mm, a wall thickness of 18.0 mm, an inside diameter of287.9 mm and a length of 500 mm. Then, one pipe end portion of eachseamless straight pipe prepared was subjected to cold pipe expanding byusing a plug identical in diameter to the plug used for cold pipeexpanding on the seamless bent pipe to increase the inside and outsidediameters of the pipe end portion. The outside diameter, inside diameterand wall thickness dimensions of the seamless straight pipes before andafter cold pipe expanding of the pipe end portion are shown in Table 2.

TABLE 2 Pipe end portion of seamless straight pipe Outside diameter Wallthickness Inside diameter (mm) (mm) (mm) ODb WTb IDb Before pipe 323.918.0 287.9 expanding After pipe 325.3 18.0 289.3 expanding

As the results shown in Table 1 and Table 2 indicate, the difference inpipe end inside diameter dimension between the seamless bent pipe andseamless straight pipes after cold pipe expanding was as small as 0.1mm. It was also confirmed that the wall thickness of the seamless bentpipe and that of the seamless straight pipes were hardly varied by coldpipe expanding.

Thereafter, a welded component comprising a seamless bent pipe andseamless straight pipes was prepared by abutting a pipe end of eachseamless straight pipe after cold pipe expanding to each end of theseamless bent pipe after cold pipe expanding and by circumferential buttwelding thereof.

In this example, the pipe end portions of the seamless bent pipe and therespective pipe end portions of the seamless straight pipes wereexpanded in diameter by cold pipe expanding alone. It is also possible,however, to subject them once to cold diameter reduction working andthen to cold pipe expanding so that the dimensional accuracy may furtherbe improved.

INDUSTRIAL APPLICABILITY

The methods according to the present invention can provide a seamlessbent pipe identical in inside diameter to a straight pipe for a linepipe and a welded component comprising such a seamless bent pipe and aseamless straight pipe at one or each end of the seamless bent pipe,without unnecessarily increasing the wall thickness of the seamless bentpipe and without internally machining the pipe end portions of theseamless bent pipe after the manufacturing thereof. The seamless bentpipe and the welded component thus obtained are excellent inconstruction performance at the site of laying line pipes and thereforecan be applied widely.

What is claimed is:
 1. A method of manufacturing a seamless bent pipe bybending a seamless straight pipe, wherein said seamless straight pipe,except for pipe end portions, is subjected to hot bending or coldbending and then straight pipe sections at pipe end portions that arenot hot or cold bent are subjected to cold pipe expanding.
 2. The methodof manufacturing the seamless bent pipe according to claim 1, whereinsaid straight pipe sections at pipe end portions are subjected to colddiameter reduction working prior to cold pipe expanding.
 3. A method ofmanufacturing a welded component comprising a seamless bent pipe and aseamless straight pipe at one or each end of said seamless bent pipe,wherein said seamless bent pipe according to claim 1 or said seamlessbent pipe manufactured by the method of claim 1 is used, and a pipe endof said seamless straight pipe which is to be welded to one or each endof said seamless bent pipe is subjected to cold pipe expanding to makethe inside diameter thereof identical to the inside diameter of saidseamless bent pipe and then said pipe end of the seamless bent pipe andsaid pipe end of said seamless straight pipe are joined together bycircumferential welding.
 4. The method of manufacturing the weldedcomponent comprising the seamless bent pipe and the seamless straightpipe at one or each end of said seamless bent pipe according to claim 3,wherein said pipe end portion of said seamless bent pipe and said pipeend portion of said seamless straight pipe are both subjected to coldpipe expanding using plugs identical in diameter.
 5. The method ofmanufacturing the welded component comprising the seamless bent pipe andthe seamless straight pipe at one or each end of said seamless bent pipeaccording to claim 3, wherein said pipe end portion of said seamlessstraight pipe is subjected to cold diameter reduction working prior tocold pipe expanding.